1. Field of the Invention
The present invention relates generally to a digital control system for an internal combustion engine, and more particularly to an initializing routine stored in a memory unit provided in the control system which includes sensors for detecting engine operating parameters, a multiplexer for selecting a sequence of the detected parameters, an A-D converter for converting the detected engine operating parameters from analog to digital, an input register for storing the digital parameter signals, an arithmetic unit for computing engine controlling values based on the values in the input register, an output register for storing the arithmetic operation results, an output unit for outputting the engine controlling values in accordance with output-command timing signals, and a memory unit for storing programs, routines, etc.
2. Description of the Prior Art
The background of the present invention will be particularly explained with respect to its application to a digital control system.
A digital control system may be used for controlling an internal combustion engine. In this case, various sensors are used for detecting various engine operating parameters, and the analog inputs of the sensors are supplied in order into an A-D converter to convert the analog inputs into digital inputs through a multiplexer which can select the respective channels of the analog inputs in accordance with a program stored in the memory. The information thus converted by the A-D converter is next processed by an arithmetic unit in cooperation with an input register and an output register in accordance with the programs stored in the memory. The arithmetic outputs thus executed are then taken out in order through an output unit in accordance with output-command timing signals to control the engine.
In the digital control system as mentioned above, the times necessary for arithmetic operations to determine the respective control value vary according to engine operating parameters, and also the output timings after the arithmetic operations are completed vary according to engine operating conditions. In other words, different conversion times and different arithmetic operation times are required according to the respective engine operating parameters in the operation processes from input to output. Therefore, various timing signals are necessary for this control system. However, immediately after the control system begins to operate, the input timing for receiving information from the sensor may not be synchronized with the respective output timing to drive an actuator. Consequently, the completion of input conversion is not synchronized with the start of arithmetic operation, nor is the completion of arithmetic operation synchronized with the timing of output. As a result, problems are encountered immediately after the engine is started because the control system is not yet working stably. Among these problems, the first is uncertainty in the arithmetic results due to the fact that the arithmetic operations start before the input information becomes stable. Another is uncertainty in the output results due to the fact that the output-command timing signal is given to the output unit before the output value is determined stably.